Liquid crystal display devices

ABSTRACT

Fringe field switching mode liquid crystal display (FFS LCD) devices are disclosed. A first substrate is disposed opposing a second substrate with a gap therebetween. A liquid crystal layer is interposed between the first and the second substrate. A gate line and data lines are formed on the first substrate in a matrix configuration and defining pixel areas. A counter electrode is disposed on each pixel area of the first substrate. A pixel electrode is disposed above the counter electrode with an insulating layer therebetween. The pixel electrode includes a plurality of parallel electrodes. Each electrode includes a first segment, a second segment, and a third segment, wherein the first segment has an included angle θ from the horizontal direction, the second segment has an included angle φ from the horizontal direction, and the first segment has an included angle θ from the horizontal direction.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of pending U.S. patentapplication Ser. No. 12/502,253, filed Jul. 14, 2009 and entitled“LIQUID CRYSTAL DISPLAY DEVICES.” Which is a divisional application ofpending U.S. patent application Ser. No. 11/532,982, filed Sep. 19, 2006and entitled “LIQUID CRYSTAL DISPLAY DEVICES”.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to liquid crystal display (LCD) devices, and moreparticularly to fringe field switching mode liquid crystal display(FFS-LCD) devices.

2. Description of the Related Art

Liquid crystal display (LCD) devices possess the advantages of smallsize, light weight and low power consumption, thus increasingportability and applicability in a wide variety of electronic andcommunication devices including notebook computers, personal digitalassistants (PDA), mobile phones and similar. Critical features forlarge-scale monitors and high-end TV applications, include fastresponse, high contrast ratio, high transparency, and wide viewing anglewithout gray scale inversion. In-plane switching (IPS) mode liquidcrystal display devices meet the above-mentioned high quality displayfeature requirements, and solve the viewing angle problems by orientingthe liquid crystal molecules to be parallel with a substrate.

Fringe field switching liquid crystal display (FFS-LCD) devices havepixel and counter electrodes comprise transparent conductors and anarrower distance between electrodes than the distance between the upperand lower substrates to form a fringe field on the electrodes. Inoperation, the fringe field on the electrodes forces the substantiallyhomogeneous liquid crystal molecules to rotate transversely between thesubstrates in which a wide viewing angle is accomplished since the lightis transmitted through the horizontally arranged liquid crystalmolecules. Moreover, since the counter electrode and the pixel electrodecomprise transparent conductive materials, the aperture ratio and thetransmittance ratio of the display devices can thereby be improved.

U.S. Pat. No. 6,856,371, the entirety of which is hereby incorporated byreference, discloses electrode structures of a conventional FFS-LCDdevice. The electrode structures are symmetrical and render high imagedisplay quality and high transmittance ratio.

FIG. 1 is a cross section of a conventional fringe field switchingliquid crystal display (FFS-LCD) device. An FFS-LCD 1 comprises a firstsubstrate (an upper substrate) 10, a second substrate (a lowersubstrate) 20, and a liquid crystal layer 30 interposed between thefirst substrate 10 and the second substrate 20, serving as an LCD cell.A counter electrode 11 and a plurality of pixel electrodes 13 aredisposed on the first substrate 10. An insulating layer 15 is disposedbetween the counter electrode 11 and the plurality of pixel electrodes13. A lower alignment layer 14 is disposed on the insulating layer 15and covers the pixel electrodes 15. A color filter layer 25 and an upperalignment layer 24 are disposed on the inner surface of the secondsubstrate 20 and adjust the liquid crystal layer 30.

FIG. 2 is a plan view of the lower substrate structure of a conventionalfringe field switching liquid crystal display (FFS-LCD) device. Twoparallel gate lines 3 and two parallel data lines 7 are orthogonallyintersected, enclosing a pixel area. A counter electrode 11 and pixelelectrodes 13 are disposed in the pixel area. The pixel electrodes 15comprise two electrode bras 13 a parallel to the data lines 7 and aplurality of inclined electrodes 13 b with an inclined angle φ. The twoends of each electrode 13 b are separately connected to the twoelectrode bras 13 a. Note that the inclined angle φ of the electrodes 13b directly affects the operating voltage of the FFS-LCD device. Morespecifically, the greater the inclination of electrodes 13 b, the higherthe voltage required to operate the FFS-LCD device.

For small FFS-LCD panels, the inclined angle φ of the electrodes 13 bmust be reduced to lower the operating voltage of the FFS-LCD device. Alow inclined angle φ of electrodes 13 b (e.g., less than 7°) can causethe disclination effect deteriorating display image quality. Conversely,high inclined angle φ of the electrodes 13 b requires a high drivingvoltage such that the physical area of the thin film transistor (TFT)must be increased to provide adequate charge storage capability. The TFTstructure comprises a gate electrode 3, a channel and source/drainregions 4, and source contact 6 a and drain contact 6 b. The draincontact 6 b connects the pixel electrodes 13 via a contact plug 9. Whenthe physical area of the thin film transistor (TFT) increases, however,the area of the pixel electrodes 13 must be reduced, thus, a smallaperture ratio and a low transmittance ratio occur.

Thus, low operating voltage FFS-LCD devices with improved aperture andtransmittance ratios, capable of preventing the disclination effect aredesirable.

BRIEF SUMMARY OF THE INVENTION

A detailed description is given in the following embodiments withreference to the accompanying drawings.

The invention is directed to electrode structures of an FFS-LCD device.The electrode structures comprise multiple deflected electrodes therebyproviding an FFS-LCD device having low operating voltage, preventing thedisclination effect and improving aperture and transmittance ratios.

Liquid crystal display devices are provided. An exemplary embodiment ofa liquid crystal display device comprises oppositely disposed first andsecond substrates with a predetermined gap therebetween. A liquidcrystal layer is interposed between the first and the second substrates.A gate line and a scan line are disposed on the first substrate in amatrix configuration and defining pixel areas. A counter electrode isdisposed on each pixel area of the first substrate. A first pixelelectrode is disposed on the counter electrode with at least oneinsulating layer therebetween. The first pixel electrode comprises aplurality of parallel electrodes, and each electrode comprises a firstsegment, a second segment, and a third segment; the first segmentincludes an angle of θ from the horizontal, the second segment includesan angle of φ from the horizontal, and the third segment includes anangle of θ from the horizontal, and wherein the angle of θ is greaterthan the angle of φ.

Note that the liquid crystal display device further comprises a secondpixel electrode disposed on the counter electrode with at least oneinsulating layer therebetween. The second pixel electrode comprises aplurality of parallel electrodes, and each electrode comprises a sixthsegment, a seventh segment, and a eighth segment. The sixth segmentincludes an angle of −θ from the horizontal. The seventh segmentincludes an angle of −φ from the horizontal. The eighth segment includesan angle of −θ from the horizontal, and the angle of −θ is greater thanthe angle of −φ.

Another exemplary embodiment of a liquid crystal display devicecomprises: oppositely disposed first and second substrates with apredetermined gap therebetween; a liquid crystal layer interposedbetween the first and the second substrates; a gate line and a scan linedisposed on the first substrate in a matrix configuration and definingpixel areas; a counter electrode disposed on each pixel area of thefirst substrate; a pixel electrode disposed on the counter electrodewith at least one insulating layer therebetween; wherein the pixelelectrode comprises a plurality of parallel electrodes, and eachelectrode comprises a first segment, a second segment, and a thirdsegment; wherein the first segment includes an angle of θ from thehorizontal, the second segment includes an angle of φ from thehorizontal, and the third segment includes an angle of θ from thehorizontal, wherein the angle of θ is greater than the angle of φ; thepixel electrode further comprises a fourth segment connecting the firstsegment of the odd electrodes and the third segment of the evenelectrodes, and fifth segment connecting the third segment of the oddelectrodes and the first segment of the even electrodes.

Some embodiments of a liquid crystal display device comprise: oppositelydisposed first second substrates with a predetermined gap therebetween;a liquid crystal layer interposed between the first and the secondsubstrates; a gate line and a scan line disposed on the first substratein a matrix configuration and defining pixel areas; a counter electrodedisposed on each pixel area of the first substrate; a pixel electrodedisposed on the counter electrode with at least one insulating layertherebetween; wherein the pixel electrode with a first portioncomprising a plurality of parallel electrodes, and each electrodecomprises a first segment, a second segment, and a third segment;wherein the first segment includes an angle of θ from the horizontal,the second segment includes an angle of φ from the horizontal, and thethird segment includes an angle of θ from the horizontal, and whereinthe angle of θ is greater than the angle of φ; wherein the pixelelectrode with a second portion comprising a plurality of parallelelectrodes, and each electrode comprises a sixth segment, a seventhsegment, and an eighth segment; wherein the sixth segment includes anangle of −θ from the horizontal, the seventh segment includes an angleof −φ from the horizontal, and the eighth segment includes an angle of−θ from the horizontal, and wherein the angle of −φ is greater than theangle of −φ.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be more fully understood by reading the subsequentdetailed description and examples with references made to theaccompanying drawings, wherein:

FIG. 1 is a cross section of a conventional fringe field switchingliquid crystal display (FFS-LCD) device;

FIG. 2 is a plan view of the lower substrate structure of a conventionalfringe field switching liquid crystal display (FFS-LCD) device;

FIG. 3 is a plan view of an electrode structure in each pixel area of anFFS-LCD device according to a first embodiment of the invention;

FIGS. 4A-4F are cross sections of the steps of fabricating the electrodestructure of an FFS-LCD device according to a first embodiment of theinvention;

FIG. 5 is a cross section of the electrode structure in each pixel areaof an FFS-LCD device taken along the line A-A′ of FIG. 3;

FIG. 6 is an equivalent circuit of the electrode structure in each pixelarea of an FFS-LCD device of FIGS. 3 and 5;

FIG. 7 is a plan view of a variation of the electrode structure in eachpixel area of an FFS-LCD device according to a first embodiment of theinvention;

FIG. 8 is a plan view of another variation of the electrode structure ineach pixel area of an FFS-LCD device according to a first embodiment ofthe invention;

FIG. 9 is a plan view of another variation of the electrode structure ineach pixel area of an FFS-LCD device according to a first embodiment ofthe invention;

FIG. 10 is a plan view of an electrode structure in each pixel area ofan FFS-LCD device according to a second embodiment of the invention; and

FIG. 11 is a plan view of an electrode structure in each pixel area ofan FFS-LCD device according to a third embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The following description is of the best-contemplated mode of carryingout the invention. This description is made for the purpose ofillustrating the general principles of the invention and should not betaken in a limiting sense. The scope of the invention is best determinedby reference to the appended claims.

FFS-LCD devices comprising electrode structures with multiple deflectedelectrodes are provided. The provided FFS-LCD devices have low operatingvoltage, thus, the disclination effect is prevented and the apertureratio and transmittance ratio are improved.

First Embodiment

FIG. 3 is a plan view of an electrode structure in each pixel area of anFFS-LCD device according to a first embodiment of the invention. In theactive matrix array substrate 101 a of FIG. 3, a unit electrodestructure comprises a plurality orthogonally intersecting gate lines 103and scan lines 107 disposed on a substrate 100. A plurality of pixelareas are defined by two adjacent gate lines 103 and scan lines 107. Acounter electrode 105 is disposed on the substrate 100 and in each pixelarea. A first pixel electrode 113 is disposed on the counter electrode105 with at least one insulating layer (referring to the firstinsulating layer 109 and the second insulating layer 110 of FIG. 5)therebetween, wherein the first pixel electrode 113 comprises twoelectrode bars 113 a parallel to the scan lines 107 and a plurality ofparallel electrodes 113 b. Each electrode 113 b comprises a firstsegment 113 b 1, a second segment 113 b 2, and a third segment 113 b 3.The first segment 113 b 1 includes an angle of θ from the horizontal.The second segment 113 b 2 includes an angle of φ from the horizontal.The third segment 113 b 3 includes an angle of θ from the horizontal.The angle of θ is greater than the angle of φ. For example, the angle ofθ is approximately in a range between 1° and 80° and the angle of φ isapproximately in a range between 0° and 79°. Since in the region Dneighboring the electrode bar 113 a, the angle of θ of the third segment113 b 3 deviating from the horizontal is greater than the angle of φ,the disclination effect can thus be prevented.

FIG. 3 shows a TFT device disposed at the intersection of each gate line103 and scan line 107 electrically coupled to the first pixel electrode113. The TFT device comprises a gate electrode 103, a channel andsource/drain regions 104, and source contact 106 a and drain contact 106b. The drain contact 106 b connects the first pixel electrodes 113 via acontact plug 109. By deflecting the angle of θ of the third segment 113b 3 greater than the angle of φ, the physical area of TFT device can bereduced, and the area of the first pixel electrodes 113 can nonethelessbe increased resulting in improved high aperture ratio and hightransmittance ratio.

Note that an alignment layer (not shown) which is horizontally rubbed isoptionally formed on the pixel electrode 113 of the substrate structure101 a.

FIGS. 4A-4F are cross sections of the steps of fabricating the electrodestructure of an FFS-LCD device according to a first embodiment of theinvention. Referring to FIG. 4A, a substrate 100 such a transparentglass substrate or a plastic substrate is provided. A patterned counterelectrode is formed on the substrate 100. Referring to FIG. 4B, apatterned first metal layer including gate lines 103 and commonelectrode lines 108 is formed on the substrate 100, wherein the commonelectrode lines 108 and the counter electrode 105 are operativelyelectrically connected. The gate lines 103 and common electrode line 108are parallel and made from metal materials such as aluminum (Al),molybdenum (Mo), or other conductive materials. A gate insulating layer109 is subsequently formed on the substrate 100 and covering the counterelectrode 105, gate lines 107, and the common electrode lines 108.

Referring to FIG. 4C, a patterned semiconductor layer is formed coveringpart of the gate lines 103. For example, a semiconductor island 104including an amorphous silicon island or polysilicon island is formedpart of the gate line 103 to serve as a carrier channel region. A sourceregion and a drain region are separately formed on both sides of thecarrier channel region. Referring to FIG. 4D, a patterned second metallayer is formed on the substrate 100. The patterned second metal layercomprises scan lines 107, source contact 106 a and drain contact 106 b.The second metal layer is preferably comprises metal materials such asaluminum (Al), molybdenum (Mo), or other conductive materials. A secondinsulating layer 110 (referring to FIG. 5) is deposited and patternedcreating a contact plug 109 on the drain contact 106 b.

Referring to FIG. 4F, a patterned pixel electrode structure is formed onthe second insulating layer 110 and operatively coupled the draincontact 106 b. The pixel electrode structure is disposed correspondingto the counter electrode 105 with the second insulating layer sandwichedtherebetween. The first pixel electrode structure 113 comprises twoelectrode bars 113 a parallel to the scan lines 107 and a plurality ofparallel electrodes 113 b. Each electrode 113 b comprises a firstsegment 113 b 1, a second segment 113 b 2, and a third segment 113 b 3.The first segment 113 b 1 includes an angle of θ from the horizontal.The second segment 113 b 2 includes an angle of φ from the horizontal.The third segment 113 b 3 includes an angle of θ from the horizontal.The angle of θ is greater than the angle of φ.

FIG. 5 is a cross section of the electrode structure in each pixel areaof an FFS-LCD device taken along the line A-A′ of FIG. 3. FIG. 6 is anequivalent circuit of the electrode structure in each pixel area of anFFS-LCD device of FIG. 3 and FIG. 5. Referring to FIG. 5, a storagecapacitor C_(st) and a fringe capacitor C_(f) are induced between theelectrode 131 b of the pixel electrode structure 131 and the counterelectrode 105. The capacitances of the storage capacitor C_(st) and thefringe capacitor C_(f) are increased as the overlying area between theelectrode 131 b of the pixel electrode structure 131 and the counterelectrode 105. The larger overlying area between the electrode 131 b ofthe pixel electrode structure 131 and the counter electrode 105 is, thelarger the TFT devices are required to be to provide adequate chargestorage capacity. When the physical area of the thin film transistor(TFT) device increases, however, the aperture ratio and lowtransmittance ratio of the FFS-LCD device are decreased. By deflectingthe angle of θ greater than the angle of φ, the physical area of TFTdevice can be reduced by improving the aperture ratio and hightransmittance ratio.

FIG. 7 is a plan view of a variation of the electrode structure in eachpixel area of an FFS-LCD device according to a first embodiment of theinvention. In the active matrix array substrate 101 b of FIG. 7, theelectrode structure in each pixel area is nearly identical to theelectrode structure in each pixel area of the first embodiment in FIG. 3and for simplicity its detailed description is omitted. The electrodestructure in each pixel area in FIG. 7 is different from the electrodestructure in each pixel area in FIG. 3 in that a second pixel electrode123 comprises a plurality of electrodes 113 b. Each electrode 113 bcomprises a first segment, a second segment, and a third segment. Thefirst segment includes an angle of −θ from the horizontal. The secondsegment includes an angle of −φ from the horizontal. The third segmentincludes an angle of −θ from the horizontal. The angle of −θ is greaterthan the angle of −φ.

FIG. 8 is a plan view of another variation of the electrode structure ineach pixel area of an FFS-LCD device according to a first embodiment ofthe invention. In FIG. 8, the first pixel electrode 113 and the secondpixel electrode 123 are mirror symmetrical horizontally.

FIG. 9 is a plan view of another variation of the electrode structure ineach pixel area of an FFS-LCD device according to a first embodiment ofthe invention. In FIG. 9, the first pixel electrode 113 and the secondpixel electrode 123 are vertically and symmetrically mirrored.

Second Embodiment

FIG. 10 is a plan view of an electrode structure in each pixel area ofan FFS-LCD device according to a second embodiment of the invention.Referring to FIG. 10, in order to improve the aperture ratio andtransmittance ratio of the FFS-LCD device, the active matrix arraysubstrate 101 c of the second embodiment of the invention comprises aplurality of orthogonally intersecting gate lines 103 and scan lines 107disposed on a substrate 100. A plurality of pixel areas are defined bytwo adjacent gate lines 103 and scan lines 107. A counter electrode 105is disposed on the substrate 100 and in each pixel area. A pixelelectrode 133 is disposed on the counter electrode 105 with at least oneinsulating layer therebetween. The pixel electrode 133 comprises anupper portion which comprises a plurality of parallel electrodes. Eachelectrode comprises a first segment, a second segment, and a thirdsegment. The first segment includes an angle of θ from the horizontal.The second segment includes an angle of φ from the horizontal. The thirdsegment includes an angle of θ from the horizontal. The angle of θ isgreater than the angle of φ. The pixel electrode 133 further comprises alower portion which comprises a plurality of parallel electrodes. Eachelectrode comprises a sixth segment, a seventh segment, and an eighthsegment. The sixth segment includes an angle of −θ from the horizontal.The seventh segment includes an angle of −φ from the horizontal. Theeighth segment includes an angle of −θ from the horizontal. The angle of−θ is greater than the angle of −φ. Note that the first portion of thepixel electrode and the second portion of the pixel electrode arevertically and symmetrically mirrored.

Third Embodiment

FIG. 11 is a plan view of an electrode structure in each pixel area ofan FFS-LCD device according to a third embodiment of the invention.Referring to FIG. 11, in order to improve the aperture ratio andtransmittance ratio of the FFS-LCD device, the active matrix arraysubstrate 101 d of the third embodiment of the invention comprises aplurality of orthogonally intersecting gate lines 203 scan lines 207disposed on a substrate 200. A plurality of pixel areas are defined bytwo adjacent gate lines 203 and scan lines 207. A counter electrode 205is disposed on the substrate 200 and in each pixel area. A pixelelectrode 213 is disposed on the counter electrode 205 with at least oneinsulating layer therebetween. The pixel electrode 213 comprises aplurality of parallel electrodes 213 b. Each electrode 213 b comprises afirst segment 213 b 1, a second segment 213 b 2, and a third segment 213b 3. The first segment 213 b 1 includes an angle of θ from thehorizontal. The second segment 213 b 2 includes an angle of φ from thehorizontal. The third segment 213 b 3 includes an angle of θ from thehorizontal. The angle of θ is greater than the angle of φ. The pixelelectrode 213 further comprises a fourth segment 213 a 1 connecting thethird segment 213 b 3 of the odd electrodes and the third segment 213 b3 of the even electrodes, and fifth segment 213 a 2 connecting the firstsegment 213 b 1 of the odd electrodes and the first segment 213 b 1 ofthe even electrodes. More specifically, the pixel electrode 213 is anS-shaped continuous zigzag line or an inverted S-shaped continuouszigzag line. Preferably the angle of θ is approximately in a rangebetween 1° and 80° and the angle of φ is approximately in a rangebetween 0° and 79°. Since in the region D neighboring the electrode bar113 a, the angle of θ of the third segment 113 b 3 deviated from thehorizontal is greater than the angle of φ, the disclination effect canthus be prevented.

Furthermore, since a first opening 213 c is formed between each adjacentfourth segments 213 a 1 and a second opening 213 c between each adjacentfifth segments 213 a 2 of the pixel electrode 213 to increase apertureratio and transmittance ratio of the FFS-LCD device. Preferably thewidth of the first and the second openings 213 c is about 0.1 μm to 10μm.

Referring to FIG. 11, a TFT device is disposed at the intersection ofeach gate line 203 and scan line 207 and electrically coupled to thepixel electrode 213. The TFT device comprises a gate electrode 203, achannel and source/drain regions 204, and source contact 206 a and draincontact 206 b. The drain contact 206 b connects the pixel electrodes 213via a contact plug 209. By deflecting the angle of θ of the thirdsegment 213 b 3 greater than the angle of φ, the physical area of TFTdevice can be reduced, and the area of the pixel electrodes 213 cannonetheless be increased resulting in improved high aperture ratio andhigh transmittance ratio.

Note that an alignment layer (not shown) which is horizontally rubbed isoptionally formed on the pixel electrode 213 of the substrate structure101 d.

While the invention has been described by way of example and in terms ofthe preferred embodiments, it is to be understood that the invention isnot limited to the disclosed embodiments. To the contrary, it isintended to cover various modifications and similar arrangements (aswould be apparent to those skilled in the art). Therefore, the scope ofthe appended claims should be accorded the broadest interpretation so asto encompass all such modifications and similar arrangements.

1. A liquid crystal display device, comprising: a first substrate and asecond substrate opposing each other with a predetermined gaptherebetween; a liquid crystal layer interposed between the first andthe second substrates; a gate line and a data line disposed on the firstsubstrate in a matrix configuration and defining pixel areas; a counterelectrode disposed on each pixel area of the first substrate; a pixelelectrode disposed on the counter electrode with at least one insulatinglayer therebetween; wherein the pixel electrode with a first portioncomprising a plurality of parallel electrodes, and each parallelelectrode comprises a first segment, a second segment, and a thirdsegment; wherein the first segment includes an angle of −θ from thehorizontal, the second segment includes an angle of −φ from thehorizontal, and the third segment includes an angle of −θ from thehorizontal, and wherein the angle of −θ is greater than the angle of −φ;wherein the pixel electrode with a second portion comprising a pluralityof parallel electrodes, and each parallel electrode comprises a sixthsegment, a seventh segment, and a eighth segment; wherein the sixthsegment includes an angle of θ from the horizontal, the seventh segmentincludes an angle of φ from the horizontal, and the eighth segmentincludes an angle of θ from the horizontal, and wherein the angle of θis greater than the angle of φ; and further comprising a commonelectrode line parallel to the gate line and connecting the counterelectrode of each pixel area.
 2. The liquid crystal display device asclaimed in claim 1, wherein the first portion of the pixel electrode andthe second portion of the pixel electrode are symmetrical and verticallymirrored.
 3. The liquid crystal display device as claimed in claim 1,further comprising a thin film transistor disposed at an intersection ofeach gate line and data line and electrically couple to the first pixelelectrode.
 4. The liquid crystal display device as claimed in claim 1,wherein the first pixel electrode further comprises two electrodesegments parallel to the data lines, and wherein one of the twoelectrode segments connects the first segment of each parallelelectrode, and the other electrode segment connects the third segment ofeach parallel electrode.
 5. The liquid crystal display device as claimedin claim 1, wherein the angle of θ is approximately in a range between1° and 80°.
 6. The liquid crystal display device as claimed in claim 1,wherein the angle of φ is in an approximate range of between 0° and 79°.7. The liquid crystal display device as claimed in claim 1, furthercomprising an alignment layer disposed on the first pixel electrode ofthe first substrate and rubbed horizontally.